What is the Btu?

• A. The amount of heat required to raise the temperature of 1 pound of water by 5 degrees Fahrenheit
• B. The amount of heat required to raise the temperature of 1 pound of water by 1 degree Fahrenheit
• C. The energy content of one cubic foot of gas
• D. The amount of heat released when gas burns completely

Answer: (D)

The Btu is a unit of energy used to measure heat. It is defined as the amount of heat required to raise the temperature of 1 pound of water by 1 degree Fahrenheit at standard atmospheric pressure. In practice, you’ll see Btu used to express fuel energy content (for example, Btu per cubic foot for natural gas), but the fundamental meaning of a Btu is this amount of heat needed to raise 1 lb of water by 1°F. The option describing heat released when gas burns completely refers to the energy obtainable from combustion (the heating value), which is related but not the basic definition of a Btu.